1. Field of the Invention
The present invention relates generally to a drug delivery apparatus and method for selectively and locally delivering a drug to internal body tissue. More particularly, the present invention relates to an apparatus and method which can both dilate a passageway and deliver a drug selectively and locally to internal body tissue after or during dilatation using a single catheter.
2. Description of the Prior Art
Many techniques currently exist for delivering drugs or other medicaments to body tissue. These include, among possible others, oral administration, injection directly into body tissue such as through an intramuscular injection or the like, topical or transcutaneous administration where the drug is passively absorbed, or caused to pass, into or across the skin or other surface tissue and intravenous administration which involves introducing a selected drug directly into the blood stream.
Except for topical or transcutaneous administration, the above drug delivery systems tend to be systemic. In other words, administration of the drug is delivered throughout the body by the blood stream. Although transcutaneous drug delivery systems tend to be localized delivery systems in that the drug is delivered locally to a selected area, such drug delivery systems are also, by definition, limited to application of a drug externally through the patient's skin or other surface tissue. Thus, the above described drug delivery systems are generally not appropriate for the localized treatment of internal body tissue.
Although many medical situations are satisfactorily treated by the general systemic administration of a drug, there are a great many treatments which could be facilitated and/or improved by the ability to deliver or administer a drug locally to a selected portion of internal body tissue, without appreciably affecting the surrounding tissue.
One example is the ability to treat the dilated vessel in percutaneous transluminal coronary angioplasty (PTCA), and thus limit or prevent restenosis. In PTCA, catheters are inserted into the cardiovascular system under local anesthesia and an expandable balloon portion is then inflated to compress the atherosclerosis and dilate the lumen of the artery. Despite the general success of such PTCA procedures, high restenosis rates (reported to be as high as 47%) continue to be a major problem. Various techniques have been tried to treat stenosed vessels including the use of lasers, application of heat and the use of intravascular stents. However, many of these are still under investigation with mixed results, while others have generally not been successful. The ability to administer a drug locally to the dilated portion of the artery in PTCA procedures, without significantly affecting other tissues, would greatly enhance the ability to address the restenosis problem.
A second example of specific application for a local drug delivery system for delivering a drug to an internal body tissue is in the treatment of cancerous tumors or the like. In the treatment of such tumors, an objective is to administer the cancer drug so that it localizes, as much as possible, in the tumor itself. Such drugs are commonly administered systemically through the blood stream. Various means are then utilized for causing the drug to localize in the cancer tumor. Nevertheless, significant portions of the drug still circulate through the blood stream, thereby affecting noncancerous tissue, producing undesirable side effects, and limiting the dosages of the drug which can be safely administered.
Furthermore, although devices are known which can provide for localized internal delivery of drugs or other substances and other devices are known which can perform dilatation of passageways, neither devices can typically be used to perform both dilatation and drug delivery.
Dilatation catheters cannot typically be used to deliver drugs because catheters which can be dilated typically consist of nonporous thermoplastic tubes molded into balloon geometries. The balloons are typically non-porous to allow for inflation with a fluid at pressures of up to 20 atmospheres without leakage of the fluid into the dilated vessel. Once the vessel is dilated, the non-porous balloon is removed and replaced with a device which is capable of delivering drug to the localized area. Such an exchange of the dilatation catheter with the appropriate drug delivery catheter results in additional time and expense, as well as overcoming the difficulties associated with returning the drug delivery catheter to the exact position of the balloon catheter when the original dilation was performed. Additionally, the time lapse between dilation and drug delivery can be significant if it affects the efficacy of the drug treatment.
Devices which can provide localized internal drug delivery have included a number of designs. Initial versions were simply dilatation catheters with a limited number of relatively large holes punched in the non-porous dilatation balloon material to render it porous. Although these balloons were capable of transferring drugs to a local internal area, they are ineffective at dilatation because of the large leakage through the pores punched through the balloons.
One attempt at providing a catheter for both dilatation and drug delivery has included coating a dilatation balloon with a drug containing matrix or microparticles which burst upon pressure to release a drug locally within a patient. In this design, the drug is exposed to the body throughout the procedure, including advancement of the catheter through the patient's body, thus offering the possibility of inadvertent and unwanted drug delivery during advancement of the catheter.
Yet another attempt includes the use of concentric porous and non-porous balloons in which the inner non-porous balloon is inflated to provide the dilatation and a drug is then provided to the space between the inner non-porous balloon and the outer porous balloon to provide local internal drug delivery. Such devices suffer from the complexity of manufacturing such a dual concentric balloon structure as well as the relatively large deflated profile of the balloon which can add to difficulties in placing the device within smaller vessels in patients.
Accordingly, there is a need in the art for a method and single apparatus which can both dilate a passageway and deliver a drug or other substance selectively and locally to internal body tissue after or during dilatation using a single catheter balloon which can be selectively made permeable.